1. Field of the Invention
The present invention relates to a method for controlling the heating of an extrusion device of a semi-finished product made of elastomeric material.
Preferably, the above-mentioned method is carried out in a process for building a component made of elastomeric material of a tyre for vehicle wheels.
2. Description of the Related Art
Throughout the following description and in the subsequent claims, the expression “elastomeric material” is used to indicate a composition comprising at least one elastomeric polymer and at least one reinforcing filler. Preferably, such composition further comprises additives such as, for example, a cross-linking agent and/or a plasticizer. Thanks to the presence of the cross-linking agent, such material may be cross-linked by heating, so as to make the end product.
The expression “semi-finished product made of elastomeric material”, on the other hand, is used to indicate an elongated element made of elastomeric material only and having a flat shape.
The expression “component made of elastomeric material” is used to indicate any component of the tyre, or a part thereof, obtained from said semi-finished product and thus comprising elastomeric material only.
Throughout the present description and in the subsequent claims, “thermal inertia” of a structural unit of an extrusion device indicates the tendency of a structural unit to withstand changes in temperature; it is higher when the mass of material constituting such structural unit is greater.
On the other hand, “working temperature” of a structural unit of the extrusion device indicates the temperature at which such structural unit is maintained during the extrusion process. This implies that at temperatures lower than the operating one, the extrusion process does not take place.
As known, a tyre for vehicle wheels generally comprises a carcass structure comprising at least one carcass ply formed of reinforcing cords incorporated in an elastomeric matrix. The carcass ply has end edges respectively engaged with annular anchoring structures. The latter are arranged in the areas of the tyre usually identified by the name “beads” and they are normally formed each by a substantially circumferential annular insert on which at least one filling insert is applied, in a radially outer position thereof. Such annular inserts are commonly identified as “bead cores” and have the task of keeping the tyre firmly fixed to the anchoring seat specifically provided in the rim of the wheel, thus preventing, in operation, the radially inner end edge of the tyre coming out from such a seat.
At the beads specific reinforcement structures may be provided having the function of improving the torque transmission to the tyre.
In tyres devoid of inner tube, called “tubeless”, an airtight coating layer made of elastomeric material, typically called liner, is typically provided in a radially inner position with respect to the carcass ply/plies.
In a radially outer position with respect to the carcass structure, on the other hand, a belt structure is associated.
The belt structure comprises one or more belt layers arranged radially one on top on the other and having textile or metallic reinforcement cords arranged preferably according to an inclined orientation with respect to the circumferential direction of the tyre and normally crossed with respect to the cords of the possible adjacent belt layer.
The belt structure can further comprise at least one reinforcing structure defined by at least one continuous reinforcing elongated element including at least one textile or metallic reinforcement cord incorporated in a matrix of elastomeric material and extending parallel to the longitudinal direction of the elongated element itself.
Between the carcass structure and the belt structure a layer of elastomeric material, called “under-belt”, can be provided, said layer having the function of making the radially outer surface of the carcass structure as uniform as possible for the subsequent application of the belt structure.
In a radially outer position with respect to the belt structure a tread band is applied, also made of elastomeric material, as well as other structural elements making up the tyre.
Respective sidewalls of elastomeric material are also applied on the side surfaces of the carcass structure, each extending from one of the side edges of the tread band up to the respective annular anchoring structure to the beads.
From the above description it is clear that a tyre for vehicle wheels typically comprises a plurality of components made of elastomeric material only, according to the definition given above. Among them the following components can be identified, as non-limiting examples: tread band, sidewalls, the so-called under-belt and/or under-layer layers, filling inserts of the annular anchoring structures, liner, sub-liner, sidewall inserts, reinforcing inserts, etc.
The above-mentioned components may be made starting from semi-finished products made of elastomeric material only, obtained by an extrusion process. The extruded semi-finished product is then laid on a forming support which can rotate about a rotation axis, so as to obtain a deposition preferably according to adjacent and/or at least partly superimposed coils, depending on the component to be made.
Typically, the extrusion process is carried out in a device consisting of a plurality of structural units having different mass, thermal inertia and working temperature, where at least some structural units having low mass and thermal inertia have a high working temperature and vice versa.
Prior to feeding the elastomeric material into the extrusion device, all of the above structural units are brought to the respective working temperature.
WO 2006/037369, in the name of the Applicant, recites that in a process for manufacturing an elastomeric tyre component, the elastomeric component is fed to an extruding device comprising a plurality of units each having a respective working temperature. Said units are heated to reach the respective working temperature, starting from the unit having the lowest working temperature up to the unit having the highest working temperature.